1. Technical Field
The present invention relates to a disc brake apparatus equipped with a parking brake mechanism.
2. Background Art
Japanese Patent Public Disclosure No. 2003-83373 discloses a disc brake apparatus equipped with a parking brake mechanism, which controls parking brake by an electric motor. The disc brake apparatus disclosed in Japanese Patent Public Disclosure No. 2003-83373 is configured so as to perform a parking brake release operation to release a parking brake applied state in response to, for example, a switch operation of a driver. The release operation is set to end by stopping a rotation of the electric motor when a predetermined time has elapsed from the switch operation as a time period in which the motor is driven to rotate in a release direction to retract a thrust member (a ramp body), which thrusts a piston.
However, according to the disc brake apparatus disclosed in Japanese Patent Public Disclosure No. 2003-83373, a constant time is set as a time period in which the electric motor is driven to rotate during the parking brake release operation. Therefore, it is difficult to appropriately set the motor rotation driving time for the release operation due to a mechanical structural variation in the dimension and a temperature characteristic. In particular, according to the disc brake apparatus disclosed in Japanese Patent Public Disclosure No. 2003-83373, a rotational amount of the motor may be insufficient or excessive during the parking brake release operation. For example, in a case where the electric motor rotates excessively, a too much clearance amount is generated between the piston and the thrust member. Therefore, this exceedance leads to a problem of the necessity of a longer time at the time of the next parking brake application operation. On the other hand, in a case where the electric motor rotates by an insufficient amount, the piston and the thrust member cannot secure a sufficient clearance amount therebetween. Therefore, this shortage leads to a problem of occurrence of a so-called drag, i.e., such a phenomenon that, even when the piston is supposed to be retracted via the brake pad according to a face deflection of the disc rotor while the vehicle is running, the piston is blocked from being retracted by the thrust member, resulting in the disc rotor and the brake pad maintained in contact with each other.